1. Field of the Invention
The invention relates to a speed variation mechanism and, more particularly, to a speed variation mechanism capable of providing different moving speeds to drive an optical device.
2. Description of the Related Art
In an optical communication apparatus (e.g., an optical switch, a tunable optical attenuator or a tunable filter) having a movable mechanical structure, a linear driving mechanism capable of providing quick and precise positioning functions is required to reduce optical signal loss during the switching process.
The optical device sometimes has to be moved at different speeds according to the moving distance and the rotation angle. If a stepping motor is used to directly drive the optical device in the optical communication apparatus, the response speed is slow because: (a) a positioning device has to be provided with respect to the stepping motor so as to prevent the stepping motor from losing its positioning precision; and (b) the stepping motor has an upper limit of the rotation speed. Furthermore, a temporary demagnetization phenomenon may occur when the rotation speed of the motor is too high, thereby causing the stepping motor to lose steps due to the linear correlation between the rotation angle of the motor and the moving speed of the optical device. Consequently, if the moving speed of the optical device is changed by directly changing the rotation speed of the motor, the positioning precision of the optical device becomes poor because the stepping motor may lose steps at a higher rotation speed.
Another design of the linear driving mechanism utilizes the motor in conjunction with a lead screw to drive the optical device. This design can effectively prevent the stepping motor from losing steps. However, if higher positioning precision is required, the moving speed of the optical device becomes slower because a high-precision lead screw is a deceleration mechanism with a high deceleration ratio. Therefore, the optical device cannot be quickly moved to the correct position. If a variably reducing gear box capable of changing the operation speed is used, the volume thereof becomes too large and the gap between the gears may cause the difficulty in positioning precision. Furthermore, if there are too many required elements, the manufacturing and assembling costs may also increase.
In view of the above-mentioned problems, an object of the invention is to provide a speed variation mechanism capable of providing different speed deceleration ratios using a simple structure.
Another object of the invention is to provide a speed variation mechanism capable of preventing the stepping motor from losing steps.
To achieve the above-mentioned objects, the invention provides a speed variation mechanism including a base, a first sliding member, a second sliding member and a fixing device. The base has a first surface. The first sliding member is able to slide on the first surface and has a second surface. The second sliding member is able to slide on the second surface and has a third surface. The third surface is in contact with a driven member so as to drive an optical device. The fixing device selectively fixes the first sliding member to the base or the second sliding member. When the second sliding member is pushed, the speed variation mechanism of the invention can provide different moving speeds for the driven member to drive the optical device by fixing the first sliding member to the base or the second sliding member.
In one embodiment of the invention, the base may be formed with at least a first hole, and the second sliding member may be formed with at least a second hole. The fixing device may include a pin disposed in the first sliding member to selectively inserted into one of the at least a first hole and the at least a second hole.
In another embodiment of the invention, the base may include a first permanent magnet, and the second sliding member may include a second permanent magnet. The fixing device may include an electromagnet capable of changing a direction of the magnetic pole. The electromagnet is disposed in the first sliding member to selectively attract one of the first permanent magnet and the second permanent magnet.
The speed variation object of this invention is implemented by changing the slope of the contact surface between the linear driving members (i.e., the first and second sliding members) and the driven member to cause different speed ratios. Accordingly, the volume can be made small to fit into a limited space, and the response speed can be made quick. In addition, time for moving the driven member can be shortened so as to achieve the objects of quick positioning and switching.